1. Field of the Invention
This invention relates to ternary polymer blends consisting of aromatic polycarbonates, polyurethanes, and polybutylene terephthalates.
2. Description of the Prior Art
Aromatic polycarbonates, as well as other constituents of the ternary polyblend, are well known and in addition possess on the whole excellent characteristics for injection molding and for other uses as a plastic. Correction of deficiencies of the polycarbonates especially for particular uses has been sought by copolymerization, cf. German Pat. No. 1,011,148 and Belgian Pat. Nos. 546,375 and 570,531, and especially McPherson et al., U.S. Pat. No. 3,187,065, in which a mixed polycarbonate-polyurethane polymer is disclosed and claimed; blending with other polymeric additives, Goldblum, U.S. Pat. No. 3,431,224; and the addition of other compounds and stabilizers, Calkino, U.S. Pat. No. 3,498,946 and Bialous, U.S. Pat. No. 3,742,083. Improvements in the qualities of polyurethane elastomers, which also exhibit excellent individual characteristics are accomplished by such processes as the polyester based condensation of Muller et al., U.S. Pat. No. 2,729,618, and the preparation of polyether or mixed polyether and polyester based elastomers such, for example, as are disclosed and claimed in Pigott et al., U.S. Pat. No. 3,012,992. The commercially available polybutylene terephthalate can be prepared by the method of Izard et al., U.S. Pat. No. 2,597,643, by esterfying terephthalic acid with a glycol, and also displays many excellent characteristics. However, it is not so ideal for some situations and may, therefore, need to be modified by the use of fillers such as glass fibers.
It is an object of this invention to provide thermoplastic and thermoelastic polyblends of commercially available polymers having improved resistance to environmental stress cracking caused by poor solvent resistance and improved impact strength, hitherto unavailable without corresponding impairment of other acceptable characteristics of the polymers.
Another object of the invention is the provision of a ternary blend of commercially available polymers that has a high critical thickness value (i.e. avoids decreases in impact strength with increasing specimen thickness), or as otherwise expressed to provide the advantages of blends while avoiding the apparently inescapable disadvantage of blends, as with polycarbonates, of lowering the critical thickness value.